High vinylidene, or highly reactive PIB is characterized by a large percentage of terminal double bonds, preferentially greater than 70% or 80%. This provides a more reactive product, compared to regular or conventional PIB, and hence this product is also referred to as highly reactive PIB. The terms reactive or highly reactive (HR-PIB) and high vinylidene (HV-PIB) are synonymous. The basic processes for producing HR-PIB all include a reactor system, employing BF3 catalysts with one or more catalyst modifiers. Since formation of the terminal double bond is kinetically favored, short reactions times favor high vinylidene levels. The reaction is typically quenched, usually with an aqueous base solution, such as, for example, NaOH or NH4OH, before significant isomerization to internal double bonds can take place. Molecular weights are relatively low. HR—PIB having an average molecular weight of about 950-1050 is the most common product. Conversions, based on isobutylene, are kept at 75-85%, since attempting to drive the reaction to higher conversions reduces the vinylidene content through isomerization. Prior U.S. Pat. No. 4,152,499 dated May 1, 1979, prior U.S. Pat. No. 4,605,808 dated Aug. 12, 1986, prior U.S. Pat. No. 5,068,490 dated Nov. 26, 1991, prior U.S. Pat. No. 5,191,044 dated Mar. 2, 1993, prior U.S. Pat. No. 5,286,823 dated Jun. 22, 1992, prior U.S. Pat. No. 5,408,018 dated Apr. 18, 1995 and prior U.S. Pat. No. 5,962,604 dated Oct. 5, 1999 are all directed to related subject matter.
Other than the HR grades and the regular or conventional grades of PIB, a certain grade of PIB known as the enhanced grade was more recently developed. The advantage of these series of products is that the overall reactivity is high without the need for higher vinylidene content. The following patents describe enhanced or mid-range vinylidene content polyisobutylene (PIB) polymers and processes for producing them: U.S. Pat. Nos. 7,037,099; 7,091,285; 7,056,990; and 7,498,396. The products are characterized in that at least about 90% of the PIB molecules present in the product comprise alpha or beta position isomers. The vinylidene (alpha) isomer content of the product may range from 20% to 70% thereof and the content of tetra-substituted internal double bonds is very low, preferably less than about 10% or 5% and ideally less than about 1-2%. The midrange vinylidene content PIB polymer products are typically prepared by a liquid phase polymerization process conducted in a loop reactor at a temperature of at least 60° F. using a BF3/alcohol catalyst system.
U.S. Pat. No. 9,074,026 to Shaikh discloses a method of making reactive PIB in a loop reactor with low solvent levels using a BF3 alcohol catalyst system.
United States Patent Application Publication No. US2010/0298507 of Menshig et al. relates to manipulating isobutene solvent levels in a loop reactor to influence PIB polydispersity and vinylidene content. See Tables 3, 4 on page 5.
U.S. Pat. No. 7,411,104 to Yun et al. discloses a process for making HR PIB with C4 raffinate using BF3 catalyst complexed with tertiary butyl alcohol and diisopropyl ether. Reaction temperatures are below 0° C. and residence times range from 15 to 90 minutes. See Examples 1-9; note Table 2, Col. 9. The reactor appears to be a CSTR.
United States Patent Application Publication No. US2009/0023822 discloses PIB polymerization using raffinate feed wherein oxygenates are removed from the feed prior to polymerization. Polymerizations are carried out well below 0° C.
A continuing problem in the industry, especially with feedstocks that contain relatively high levels of n-butenes and butadienes such as raffinate is the persistance of fluorides in the product, especially organic fluorides. Fluorides cause numerous problems in the plant and in the product. For one, fluorides cause corrosion in a manufacturing plant, in both the aqueous and organic phases as the material is washed and worked up by purification. It is also a potential wastewater problem, depending on plant effluent standards. So also, remaining fluoride in the product is undesirable as well it may cause corrosion problems when making derivatives such as alkyl phenols or anhydrides and may be unacceptable to customers making derivatives.
Known methods of reducing residual fluorides in products based on raffinate feed are relatively complex and only marginally effective.
U.S. Pat. No. 6,300,444 to Tokumoto et al. discloses a process for making reactive PIB with residence times of from 5 minutes to 4 hours with a BF3/ether-alcohol catalyst system followed by distillation. Fluoride levels are reported to be below 30 ppm. While a range of reactor temperatures are discussed, the examples are carried out at −10° C. It is also noted that even after repeated distillation, 6 ppm organic fluoride remains in the polymer. See Table 1, column 9
U.S. Pat. No. 5,674,955 to Kerr et al. discloses a method of making PIB from raffinate by pre-treating the raffinate to reduce 1-butene and increase 2-butene. The polymerization reaction is carried out at low temperature. The pre-treatment procedure includes isomerization and is reported to reduce residual fluorides in the final product. Organic fluorides reported in the products prepared from the modified raffinate streams (batches 3, 6, 9) are reported to be above 15 ppm.
United States Patent Application Publication No. 2015/0322181 teaches to treat cracked naptha raffinate containing isobutene through hydrogenation of the butadiene, followed by isomerization of B1 to B2 isomers followed by distillation to remove linear butenes. Even after the lengthy pre-treatment, fluoride levels in the purified product remain at 3 ppm and higher.
U.S. Pat. No. 5,846,429 to Shimizu et al. discloses a method of removing BF3 from a liquid mixture by filtering with a polymer fiber having nitrile groups.